Thin film transistor (referred herein as “TFT”) is the key component of integrated circuits for electronic devices. Although organic material based TFTs generally provide lower performance characteristics than their conventional silicon counterparts, such as silicon crystal or polysilicon TFTs, they are nonetheless sufficiently useful for applications in areas where high mobility is not required. These include large area devices, such as image sensors, active matrix liquid crystal displays and low-end microelectronics such as smart cards and RFID tags. TFTs fabricated from organic or polymer materials are potentially very low cost, and may also be functionally and structurally more desirable than conventional silicon technology in the aforementioned areas in that they may offer mechanical durability, structural flexibility, compact and light weight characteristics, and the potential of being able to be incorporated directly onto the active media of the devices, thus lowering manufacturing cost and enhancing device compactness for transportability.
Currently, the most developed organic TFTs are based on pentacene and oligo or polythiophenes. The performance of these materials, in terms of mobility and current on/off ratio, now match the requirements for numerous applications such as active matrix addressing arrays for displays or basic switching and memory devices. However, most of the compounds with the desirable properties are p-type, meaning that negative gate voltages, relative to the source voltage, are applied to induce positive charges (hole) in the channel region of the devices. However, both p-type and n-type semiconductor materials are required to form a complementary circuit. Advantages of complementary circuits, compared to ordinary TFT circuits, include higher energy efficiency, longer lifetime, and better tolerance of noise.
Only a limited number of materials have been developed for the n-type component of such organic complementary circuits, because of the lack of suitable n-type organic materials and theoretical arguments which predict a reduced stability of the n-conducting radical anions under ambient conditions. There is a need, which the present invention addresses, for inventions that expand the choice of n-type semiconductor materials suitable for electronic devices.
The following documents may be relevant:
Amit Babel et al., “Electron Transport in Thin-Film Transistors from an n-Type Conjugated Polymer,” Adv. Mater. 14, No. 5, pp. 371-374 (Mar. 4, 2002), which discloses a field effect transistor made from a ladder poly(benzobisimidazobenzophenanthroline) (“BBL”) thin film where the structural formula of BBL is depicted in FIG. 1.
H. E. Katz et al., “A soluble and air-stable organic semiconductor with high electron mobility,” Nature, Vol. 404, pp. 478-480 (Mar. 30, 2000).
Patrick R. L. Malenfant et al., “N-type organic thin-film, transistor with high field-effect mobility based on a N,N′-dialkyl-3,4,9,10-perylene tetracarboxylic diimide derivative,” Applied Physics Letters, Vol. 80, No. 14, pp. 2517-2519 (Apr. 8, 2002).
Howard E. Katz et al., “Naphthalenetetracarboxylic Diimide-Based n-Channel Transistor Semiconductors: Structural Variation and Thiol-Enhanced Gold Contacts,” J. Am. Chem. Soc., Vol. 122, pp. 7787-7792 (2000).
J. H. Schon et al., “Perylene: A promising organic field-effect transistor material,” Applied Physics Letters, Vol. 77, No. 23, pp. 3776-3778 (Dec. 4, 2000).
Katz et al., U.S. Pat. No. 6,387,727 B1.
Dimitrakopoulos et al., U.S. patent application Publication No. 2002/0164835 A1.
Hor et al., U.S. Pat. No. 4,587,189.
Hor et al., U.S. Pat. No. 5,225,307.